insect breathing

[Kenelm Philip]

	Respiration in terrestrial insects is varied enough that it's
difficult to make general statements that apply across the board. The
following should apply in most cases, however.

	1) Insects take up oxygen through a complex network of trachea and
tracheoles. The trachea connect to the exterior via the spiracles, and at
their inner ends connect to the tracheoles, which form a network (often
through the body. Both trachea and tracheoles may anastomose (join one
another to form a connected system). There may also be 'air sacs' in the
system.

	2) Diffusion alone accounts for the oxygen transport through the
tracheoles, and may be the main factor in the trachea in some cases.

	3) Respiratory movements of the abdomen (and in some cases the
thorax) introduce additional oxygen into the trachea in some cases, as
grasshoppers, some beetles, etc. Wigglesworth refers to this as 'Venti-
lation control'. In some insects a directed flow of air results, with
intake through some spiracles and egress through others.

	For details, see 'The Principles of Insect Physiology', by
Wigglesworth.

							Ken Philip
fnkwp at aurora.alaska.edu